Welding attachment of anodes for cathodic protection



April 20, 1965 H. s. PREISER 3,179,582

WELDING ATTACHMENT OF ANODES FOR CATHODIC PROTECTION Filed July 26, 1961 INVENTOR I HERMAN S. PREISER BY M41 M AGENT.

United States Patent 3,179,582 WELDING ATTACHMENT 0F ANODES FOR CATHODIC PROTECTION Herman S. Preiser, Philadelphia, Pa, assignor to the United States of America as represented by the Secretar-y of the Navy Filed July 26, 1961, Ser. No. 127,067 2 Claims. (63!. 204-197) (Granted under Title 35, U.S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to the cathodic protection of corrodible materials and more particularly to the attachment of galvanic anodes to a metallic structure of a seagoing vessel for cathodically protecting the metallic structure against electrolytic corrosion.

Generally, when two dissimilar metals are immersed in an electrolyte and are in electrical contact with each other, a primary, or galvanic electric cell is established with the effect that an electric current flows from the metal having the higher order of the electronrotive series to the other metal. The action of this current causes corrosion of the metals involved. To prevent this corrosive action, it has been common practice for some time to provide a sacrificial anode in electrical contact with the metals to be protected to produce an electric current which acts to neutralize the currents produced by the metals which are to be protected. The sacrificial anodes, which may comprise bars of aluminum, magnesium, zinc, and/ or other metals having a higher order in the electromotive series than the metals to be protected, are slowly dissipated but are considered expendable since the desired action of corrosion protection is effectively accomplished.

Because of its simplicity and efiectiveness, cathodic protection of seagoing vessels has attained widespread use. The usual procedure for protecting a vessel is to attach one or several sacrificial anode bars to that portion of the ship which is normally immersed in sea water, which acts as an electrolyte.

It has been customary to simply attach the anodes to the ship by bolting the anode elements in position. However such bolting methods have not been too satisfactory inasmuch as good electrical contact between the anode and its supporting member is never a certainty and the bolting, if faulty, results in the anode giving poor performance as a corrosion protective device. Moreover, this attachment of separate anodes to the hull or other portion of the vessel generally involves a number of fabrication problems, which require large expenditures in time and labor. For example, it has been a common practice to provide cast-in protruding support straps for attaching the anode to the hull.

Another undesirable factor arising from bolting the anodes into position is the fact that the faying surfaces as well as the bolt holes of the anode must be carefully prepared with a waterproof material to prevent the anode material from dissipating and accumulating adjacent to the faying and bolt joints. .Such action causes a loosening and eventual detachment of the anode from its support. Furthermore, as the sacrificial anodes are slowly dissipated in the electrochemical action, the securing bolts which hold the anodes in position protrude above the body of the anodes. Since the anodes are attached to the vessels underbody and are immersed in sea water, the

protruding bolts increase water resistance and turbulence thereby reducing the etficiency and/ or speed of the vessel.

In instances where cast-in straps are used to secure the anodes to the hull it was necessary to confine the sacrificial action of the anode to the top surface so that the "ice strap embedment could be made as close to the faying surface as practicable.

In U.S. Patent No. 2,762,771, granted September 11, 1956, to Herman S. Preiser, it was suggested that sacrificial anodes be attached to steel surfaces by cladding, i.e., rolling the anodic material upon its metallic-supporting structure. Although this method was satisfactory for some applications it was not adaptable to aluminum hulls or for attachment directly to the hull surfaces.

An object of the present invention is to overcome the foregoing difficulties by providing an improved method and means for applying and retaining sacrificial anodes to the body of a cathodically protected aluminum structure to protect it against electrolytic corrosion.

Another object is to provide a mechanically and electrically secure method for attaching galvanic anodes to an aluminum structure.

A further object is the provision of a sacrificial anode which introduce a minimum of resistance to the underwater portions of a seagoing vessel during the life of the anode.

A still further object of the present invention is the provision of a method and means for attaching a sacrificial anode to the body of an aluminum vessel which insures intimate electrical contact between the anode and its supporting structure at all times.

Still another object is to provide a method and means for attaching an anode to the body of an aluminum vessel which eliminates the necessity of protecting the f aying and joint surfaces of the anode.

In accordance with the present invention the above objects and others are accomplished by the attachment of sacrificial anodes to an aluminumbody by use of an aluminum welding material which is more cathodic than the anode. Thus the weld will not be eroded away prior to. the erosion of the anode thereby insuring retention of the anode on the hull until the anode is completely expended. e

Other objects and many of the attendant advantages of this invention will be readily appreciated. :as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like or corresponding parts throughout the figures thereof and wherein:

FIG. 1 is a view in perspective of a portion of an aluminum ship hull with sacrificial anodes attached in ac cordance with the present invention;

FIG. 2 is a detailed view of the attached. anode shown inFIG. 1;

FIG. 3 is an alternative embodiment of an attached anode.

Referring now to the drawings wherein like reference characters designate like or corresponding parts through out the several views, there is shown in FIG. 1 an aluminum alloyhull 1-1, on the bottom of which are attached a pair of rudders 12 and a pairof propellers 13 mounted on propeller shafts 14 which are supported by propeller struts or the like 16 and 17. A pair of sacrificial anodes 18 for cathodic protection of hull 1 1 are attached to the hull along its chine.

There is shown in FIG. 2 a detailed enlarged view of one of the sacrificial anodes 18. From this figure it can be seen that anode 18 is composed of a plurality of anode sections 21, 22, and. 23 which are welded together by butt welds 24 and 25 and are secured to the hull 11 by a plurality of weld beads 26. The ends 27 and 28 of the end strips 21 and 23 respectively are rounded to reduce the water resistance caused by the anode strips.

FIG. 3 shows an enlarged detailed view of another embodiment of a sacrificial anode attached to the hull to the anode providing protection to the structure.

11. In this embodiment a single anode strip 180:, streamlined in shape, is secured to the hull 11 by a continuous light welding bead 29.

In each case the welding metal is cathodic to the anode, i.e., has a lower order in the electromotive series than the metal of the anode. The anode metal, of course, must, if it is to be efifective in preventing corrosion, be a metal having a higher order in the electromot-ive series than the metal which it is to protect. Thus, when the anode is immersed in sea water, the anode metal will be dissipated due to galvanic action in the sea water electrolyte, but the weld forms a positive electrical and mechanical connection between the hull and the anode for the life of the anode.

In a practical application of the invention, a 6061 aluminum alloy plate was cathodically protected by an aluminum zinc alloy anode structure consisting of 95 percent aluminum and Zinc with a controlled iron impurity below 0.17 percent. .The 6061 aluminum of the plate had the following composition, as defined in Federal Specification QQ-A-327 b, dated March 7, 1958:

Ingredient Min. Percent Max. Percent Ma nesium 0.80 1. Silion 0. 40 0. 80 Chromium 0. 15 0. Iron 0. 70 Copper 0. 15 0. Titanium 0. 15 Manganese a 0. 15 Zinc V 0. 25 Others, eaeh 0, 05 Others, total O. 15 Aluminum Remainder The anode was welded in a continuous light bead run along all edges of the anode; the plate using an aluminum alloy welding rod having the following composition:

It is to be understood that the above compositions are by way of example only, and that other compositions could be used equally well to practice the instant invention. In accordance with the invention the basic requirements of the material compositions are that a strong weld between the anode and the base is provided, that the anode be of a metal having a higher order in the electromotive series than the metal, which is to be protected, and that the welding material be cathodic to the anode or, in other words, he of a metal having a lower order in the electromotive series than the anode.

The alloy of the anode is simply welded in place by means of a suitable welding material which is cathodic On boat hull-s the anode is fitted, preferably in longitudinal strips, along bilge keels or chines although other locations below the waterline may be utilized. The strips may be streamlined to lower the water resistance. When two strips are joined in tandem, a slight space separates the abutting ends which can then be simultaneously welded together and Welded to the structure by one pass of the welding torch. This technique thereby eliminates unreliable bolting attachment or the necessity to provide for cast-in special supporting straps, "and eliminates prevents weld deterioration and therefore insures long operating life.

Furthermore, the cathodic protection of aluminum structures requires .a low voltage source of electrical current in order to prevent alkali corrosion of the structure. Zinc and aluminum are the only two common materials capable of accomplishing this safely and without control. By the instant invention it is possible to provide such cathodic protection to aluminum without the disadvantages encountered in prior art techniques.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In the cathodic protection of an essentially aluminum hull, a sacrificial galvanic anode comprising at least one body of aluminum alloy having an exposed surface and at least a portion of another surface of said body joined directly to the hull by a weld bead, said weld bead being composed of an aluminum alloy which is cathodic to said sacrificial anode, said weld bead consisting essentially of iron in an amount ranging from 4.56%, appreciable amounts of Zinc, copper, titanium manganese, silicon and beryllium totalling about 1.3%, the total or" other ingredients not exceeding 0.15%, and the remainder being of aluminum.

2. Apparatus according to claim 1 wherein the material of the anode consists essentially by weight of about 95% aluminum and about 5% zinc with a controlled iron impurity below 0.17%.

References Cited by the Examiner UNITED STATES PATENTS 902,758 11/08 Nicken 204-197 2,343,440 3/44 Andrus 204-197 2,619,455 11/52 Harris et al. 204-197 2,666,027 1/54 Vallett 204-197 2,756,204 7/156 Higgins 204-197 2,762,771 9/56 Preiser 204-197 2,882,213 4/59 Douglas 204-197 2,985,530 5/61 Fetzer -146 3,012,959 12/61 Barnard 204-197 3,037,925 6/62 Boncher et al. 204-197 3,048,535 8/62 Sabins 204-197 FOREIGN PATENTS 331,649 7/30 Great Britain.

OTHER REFERENCES Graham et al.: Trans. of the Soc. of Naval Architects & Marine Engrs, vol. 64, 1956, pages 275, 278 and 296.

Proc. 2d Annual Water Conference, Engr. Soc. of Western Penna, November 3, 1941, pages 15-19.

Fahrney et al.: Chem. & Metallurgical Engr., July 1942, pages 86 and 87.

WINSTON A. DOUGLAS, Primary Examiner.

JOSEPH REBOLD, MURRAY TILLMAN, JOHN H.

MACK, Examiners. 

1. IN THE CATHODIC PROTECTION OF AN ESSENTIALLY ALUMINUM HULL, A SACRIFICAL GALVANIC ANODE COMPRISING AT LEAST ONE BODY OF ALUMINUM ALLOY HAVING AN EXPOSED SURFACE AND AT LEAST A PORTION OF ANOTHER SURFACE OF SAID BODY JOINED DIRECTLY TO THE HULL BY A WELD BEAD, SAID WELD BEAD BEING COMPOSED OF AN ALUMINUM ALLOY WHICH IS CATHODIC TO SAID SACRIFICAL ANODE, SAID WELD BEAD CONSISTING ESSENTIALLY OF IRON IN AN AMOUNT RANGING FROM 4.5-6%, APPRECIABLE AMOUNTS OF ZINC, COPPER, TITANIUM MANGANESE, SILICON AND BERYLLIUM TOTALLING ABOUT 1.3%, THE TOTAL OF OTHER INGREDEIENTS NOT EXCEEDING 0.15%, AND THE REMAINDER BEING OF ALUMINUM. 